Semiconductor light-emitting devices, such as light-emitting diodes (LEDs) and laser diodes (LDs), are among the most efficient and robust light sources currently available.
Light extraction is a key issue for light emitting devices. A common problem with semiconductor light-emitting devices is that the efficiency with which light may be extracted from the device is reduced due to internal reflection in the interface between the device and the surroundings, followed by reabsorption of the reflected light in the device. The internal reflection is due to that the refractive index of the device materials is higher than the refractive index of the material in which the device is packaged or encapsulated.
For high efficient light extraction, it is advantageous if the light extracting materials are in direct contact with the light-emitting device. However, in high power applications, where single solid-state light emitting devices with an effect of up to 3 Watts per square mm or arrays of such devices, with a total effect of up to 100 Watts or more, a lot of heat is dissipated from the light emitting devices. Temperatures of up to 250° C. are easily reached for such high power application.
Thus, for high-power applications, a heat resistant encapsulation has to be used. Thus it would be advantageous to use a fully inorganic approach, as inorganic materials may be chosen that have very high temperature resistance.
JP-2003179270-A describes a semiconductor light emitting element coated directly with a translucent coating material made of polymetaloxane or ceramic and that is heat resistant.
However, the processing temperature for connecting the coating material and the light emitting element must be low, e.g. lower than 340° C., or otherwise, the n/p-junctions in the light emitting element will be damaged.
For coatings/encapsulations of ceramic materials, it would be advantageous to be able to use higher temperatures, for example to increase the range of different materials which can be used, and in steps of attaching other components, such as for example lenses, to the encapsulation.
However, substrates and circuitry on which light-emitting semiconductor devices are arranged are often heat sensitive. Thus, it would be advantageous with a device that allows for high-temperature processing of the encapsulation without damaging the substrate and/or circuitry.
For high-intensity applications, it would also be advantageous to be able to easily arrange several semiconductor light-emitting devices under one and the same encapsulation to, for example, reduce the size of the device and to improve color mixing.